He's saying that 14 or 15 "mini forums" don't have to exist. "Shouldn't" doesn't enter into it, there are no rules about this kind of thing.
It only means consolidation of power in the startrek@lemmy.world instance if everybody prefers to go there over the alternatives. If the moderators or admins there go mad with their moderate amount of power and the community there starts sucking, everyone can switch over to a different startrek on a different instance.
I thought the reason we wanted to use the Fediverse over Reddit was because Reddit had too much control over the content, but if one instance has all the content, doesn't that instance have just as much power as Reddit has now?
An instance only has power over its own self. If lemmy.world's administrators suddenly pull off their masks to reveal that they were Reddit's admins all along, everyone can just switch to using a different startrek community on a different instance.